IMPROVEMENT OF THERMAL-STABILITY OF POROUS NANOSTRUCTURED CERAMIC MEMBRANES

Unsupported crack-free lanthana-doped alumina and titania membranes an d yttria-doped zirconia membrane were prepared by the sol-gel method. A novel solution-sol doping method was employed to coat the dopant oxi de on the grain surface of these nanostructured ceramic membranes. The pore and phase structure data of these membranes after heat treatment from 450 to 1100-degrees-C under an atmosphere of air and a steam/air mixture show a substantially improved thermal and hydrothermal stabil ity of these doped ceramic membranes. Doping lanthana (in gamma-alumin a and titania membranes) and yttria (in zirconia membrane) raises the gamma-alumina to alpha-alumina, anatase to rutile, and tetragonal zirc onia to monoclinic zirconia phase transformation temperature by about 200-degrees-C (for alumina), 150-degrees-C (for titania) and 300-degre es-C (for zirconia), respectively. At temperatures lower than the phas e transformation temperatures, doping retards the surface area loss an d pore growth of the three membranes. For the three ceramic membranes investigated, the effects of stabilizing the pore structure decrease i n the following order: zirconia > titania > gamma-alumina.